In the drilling of boreholes for oil and gas wells, a well casing is typiclly placed in the borehole. The casing is typically fixed by cementing it to the formation. Cementing of the casing fixes the casing to the formation by filling the annulus between the casing and the formation. Casing cement also provides a seal between the casing and formation which prevents fluid migration along the exterior of the casing. The casing and cement are perforated to allow production of the oil or gas from the formation.
Casing packers are often employed during well completion operations as well as during production. Such packers often include provision to allow removable tubing to extend through the packer for production or completion operations. The packers provide a seal between the casing and tubing. In well workover operations or recovery enhancement operations, often materials such as steam or fracturing fluids are employed. Such materials are preferably placed within a specified zone in the formation. Typically packers or other casing sealing devices are employed to separate the casing into distinct zones to allow the materials to be pumped into the desired zone of the formation. Typically an expandable packer including radially expandable slips and a resilient packing element is placed in the desired position between the casing and a tubing string by expanding the slips and packing element to fix the packer between the casing and the tubing. As an alternative, a permanent "packer" can be constructed within the casing by placing cement within the casing in a position to seal the annular space between the casing and the injection or production tubing running inside the casing.
The seals of expandable packers are subject to deterioration and possible failure from high temperatures, high treatment pressures, high formation pressures, as well as the corrosive or caustic nature of treatment, borehole fluids or production fluid. Permanent cement packers are more resistant to high temperature and pressures than expandable resilient seal packers. However, such cement packers are often susceptible to deterioration from treatment or downhole fluids and require unique placement or setting techniques.